A series of environmental friendly acidic resists were prepared for nanoimprint lithography on flexible plastic substrates. These resists can be easily removed by an aqueous base solution at the final stripping step instead of using an organic solvent or reactive ion etching (RIE). which is used in conventional imprint processes. The resist polymers were prepared via free radical copolymerization of methylmethacrylate (MMA), n-butylacrylate (n-BA) and methacrylic acid (MAA) monomers. For use on flexible plastic substrates, the glass transition temperatures of these polymers were adjusted to a range of 25-41 degrees C according to the molar ratio of the monomers. The weight average molecular weights (Mw) of these polymers were between 30000 and 40 000 g/mole measured by GPC. Replications of high-density line and space patterns with resolution of 5 Am and 100 nm were obtained on a flexible indium tin oxide/poly(ethylene terephthalate) (ITO/PET) substrate. The subsequent ITO etching pattern was also achieved. (c) 2005 American Vacuum Society.